Missing link in the evolution of complex cells discovered

This false-color image shows a cell of thermophilic methanogenic archaea. Image credit: University of California Museum of Paleontology.
This false-color image shows a cell of thermophilic methanogenic archaea. Image credit: University of California Museum of Paleontology.

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Μελέτη, η οποία εκπονήθηκε από ερευνητική ομάδα του Πανεπιστημίου της Ουψάλα στην Σουηδία και δημοσιεύθηκε αυτήν την εβδομάδα στην επιστημονική επιθεώρηση Nature, παρουσιάζει την ανακάλυψη νέου μικροβίου, το οποίο αντιπροσωπεύει συνδετικό παράγοντα στην πολύπλοκη εξελικτική πορεία της ζωής. Παρέχει βαθύτερη κατανόηση του τρόπου με τον οποίον δισεκατομμύρια χρόνια πριν, οι σύνθετοι τύποι κυττάρων που απαρτίζουν φυτά, μύκητες καθώς επίσης ζώα και ανθρώπους, εξελίχθηκαν από απλά μικρόβια.

Η προέλευση των ευκαρυωτικών κυττάρων, παραμένει ένα από τα πλέον αμφιλεγόμενα ζητήματα στη σύγχρονη βιολογία. Πρόσφατες μελέτες, παρέχουν υποστήριξη για την ανάδυση του ευκαρυωτικού κυττάρου – ξενιστή, μέσα από τα πρώιμα στάδια της ζωής, αλλά η ταυτότητα και η φύση του υποτιθέμενου προγονικού αρχαίου νουκλεοσώματος, παραμένει θέμα συζήτησης. Στην παρούσα μελέτη περιγράφεται η ανακάλυψη του Lokiarchaeota, ενός νέου υποψηφίου της συνομοταξίας αρχαιοϊστονών, ο οποίος συνιστά μονοφυλετική ομάδα με τους ευκαρυώτες στις φυλογενετικές αναλύσεις και των οποίων το γονιδίωμα, κωδικοποιεί ένα διευρυμένο φάσμα ευκαρυωτικών πρωτεϊνών, ένδειξη εξελιγμένων ικανοτήτων αναδιαμόρφωσης της κυτταρικής μεμβράνης. Τα αποτελέσματα, ενισχύουν την υπόθεση ότι, ο ευκαρυωτικός ξενιστής εξελίχθηκε από κάποιο δεκτικό αρχαιοβακτήριο καταδεικνύοντας ότι πολλά στοιχεία που ενισχύουν τα ειδικά χαρακτηριστικά του ευκαρυώτη, ήταν ήδη παρόντα στον εν λόγω πρόγονο. Αυτά προίκισαν τον ξενιστή με πλούσιο γονιδιωματικό καταπίστευμα, ώστε να υποστηριχθεί η αύξηση της κυτταρικής και γονιδιωματικής πολυπλοκότητός του, κάτι που χαρακτηρίζει τα ευκαρυωτικά κύτταρα.
__Π.Δ.Λιβάς (απόδοση της σύνοψης που παρέχεται από το Nature)


NewsUppsala University in Sweden • May 07, 2015
by Linda Koffmar

Photograph: R.B. Pedersen, Centre for Geobiology (University of Bergen, Norge)
The microbe was found at 2,352 metres depth in the Atlantic between Norway and Greenland. Photograph: R.B. Pedersen, Centre for Geobiology (University of Bergen, Norge)

Cells are the basic building blocks of all life on our planet. Yet, whereas the cells of bacteria and other microbes are small and simple, all visible life, including us humans, is generally made up of large and complex cell types. The origin of these complex cell types has long been a mystery to the scientific community, but now researchers from Uppsala University in Sweden have discovered a new group of microorganisms that represents a missing link in the evolutionary transition from simple to complex cells.

In the 1970s, the acclaimed biologist Carl Woese discovered a completely new group of microorganisms, the Archaea, and showed that these represented a separate branch in the Tree of Life – a finding that stunned the scientific community at the time. Despite that archaeal cells were simple and small like bacteria, researchers found that Archaea were more closely related to organisms with complex cell types, a group collectively known as ‘eukaryotes’. This observation has puzzled scientists for decades: How could the complex cell types from eukaryotes have emerged from the simple cells of Archaea?

In this weeks’ edition of Nature, researchers from Uppsala University in Sweden, along with collaborators from the universities in Bergen (Norway) and Vienna (Austria) report the discovery of a new group of Archaea, the Lokiarchaeota (or ‘Loki’ for short), and identify it to be a missing link in the origin of eukaryotes.

“The puzzle of the origin of the eukaryotic cell is extremely complicated, as many pieces are still missing. We hoped that Loki would reveal a few more pieces of the puzzle, but when we obtained the first results, we couldn’t believe our eyes. The data simply looked spectacular”, says Thijs Ettema at the Department of Cell and Molecular Biology, Uppsala University, who lead the scientific team that carried out the study.

“By studying its genome, we found that Loki represents an intermediate form in-between the simple cells of microbes, and the complex cell types of eukaryotes”, says Thijs Ettema.

When Loki was placed in the Tree of Life, this idea was confirmed.

“Loki formed a well-supported group with the eukaryotes in our analyses”, says Lionel Guy, one of the senior scientists involved in the study from Uppsala University.

“In addition, we found that Loki shares many genes uniquely with eukaryotes, suggesting that cellular complexity emerged in an early stage in the evolution of eukaryotes”, says Anja Spang, researcher at Department of Cell and Molecular Biology , Uppsala University, and one of the lead-authors of the study.

The name Lokiarchaeota is derived from the hostile environment close to where it was found, Loki’s Castle, a hydrothermal vent system located on the Mid-Atlantic Ridge between Greenland and Norway at a depth of 2,352 meters.

“Hydrothermal vents are volcanic systems located at the ocean floor. The site where Loki is heavily influenced by volcanic activity, but actually quite low in temperature”, says Steffen Jørgensen from the University of Bergen in Norway, who was involved in taking the samples where Loki was found.

“Extreme environments generally contain a lot of unknown microorganisms, which we refer to as microbial dark matter”, says Jimmy Saw, researcher at Department of Cell and Molecular Biology, Uppsala University, and co-lead author of the paper.

By exploring microbial dark matter with new genomics techniques, Thijs Ettema and his team hope to find more clues about how complex cells evolved.

“In a way, we are just getting started. There is still a lot out there to discover, and I am convinced that we will be forced to revise our biology textbooks more often in the near future”, says Thijs Ettema.

Provided by Uppsala University

Research paper

Complex archaea that bridge the gap between prokaryotes and eukaryotes – Nature(2015)doi:10.1038/nature14447

Further Information

Dec. 1997, p. 456–502 Vol. 61, No. 4
Copyright © 1997, American Society for Microbiology
-Archaea and the Prokaryote-to-Eukaryote Transition
Canadian Institute for Advanced Research, Department of Biochemistry, Dalhousie University, Halifax, Nova Scotia, Canada, and Department of Bioinformatics, SmithKline Beecham Pharmaceuticals, Collegeville, Pennsylvania
_read through dowloaded pdf (47pages)  Microbiol. Mol. Biol. Rev.-1997-Brown-456-502, or clicking here

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press release through SciLifeLab


Spang, A., Saw, J., Jørgensen, S., Zaremba-Niedzwiedzka, K., Martijn, J., Lind, A., van Eijk, R., Schleper, C., Guy, L., & Ettema, T. (2015). Complex archaea that bridge the gap between prokaryotes and eukaryotes Nature DOI: 10.1038/nature14447